\(If a^2 + b^2 = 111 ,\) a × b = 27, and  a > b, find the value of \(\frac{a -b}{a+b}\)

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RRB NTPC Graduate Level CBT-I Official Paper (Held On: 06 Jun, 2025 Shift 2)
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  1. \(\sqrt{\frac{53}{165}}\)
  2. \(\frac{57}{165} \)
  3. \(\sqrt{\frac{57}{165}} \)
  4. \(\frac{53}{165} \)

Answer (Detailed Solution Below)

Option 3 : \(\sqrt{\frac{57}{165}} \)
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Detailed Solution

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Given:

a2 + b2 = 111

a × b = 27

a > b

Formula used:

(a - b)2 = a2 + b2 - 2ab

(a + b)2 = a2 + b2 + 2ab

Calculations:

First, find the value of (a - b)2:

(a - b)2 = a2 + b2 - 2ab

⇒ (a - b)2 = 111 - 2 × 27

⇒ (a - b)2 = 111 - 54

⇒ (a - b)2 = 57

Since a > b, (a - b) must be positive:

⇒ a - b = \(\sqrt{57}\)

Next, find the value of (a + b)2:

(a + b)2 = a2 + b2 + 2ab

⇒ (a + b)2 = 111 + 2 × 27

⇒ (a + b)2 = 111 + 54

⇒ (a + b)2 = 165

Assuming a + b is positive (as implied by the options):

⇒ a + b = \(\sqrt{165}\)

Now, find the value of \(\frac{a - b}{a + b}\):

\(\frac{a - b}{a + b} = \frac{\sqrt{57}}{\sqrt{165}}\)

\(\frac{a - b}{a + b} = \sqrt{\frac{57}{165}}\)

∴ The value of \(\frac{a - b}{a + b}\) is \(\sqrt{\frac{57}{165}}\).

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